Does transfomer is symbol of richness in Amplifiers? what about SMPS

[greenhorn]

Take a case of class-A amp with 50 watts. Ignore the COSTS. Look at it from technical point of view with following points.

Class A is a niche case. But yes, For class A, an SMPS makes a lot of sense as the power drawn by a class A does not vary as much as a class AB.

Another Place where you need a switching power supply is in car audio amplifiers. If you need anything more than 17W or so RMS, you need higher voltages, so step up DC SMPS are used. This is one of those cases where a Linear PSU CANNOT be used

 

[kanwar]

Okay thanks but there is another school of thought I came across, there are some products like JKDAC32 which uses built in battery and claim that it gives much purer form of the myth named "linear power". In fact JKDAC32 now offers a add-on module which trickle charges its battery while in use. Would this not be a better and cheaper option that costly linear power supplies?

Using floating battery power is easy way of getting rid from the mains induced hum and where applications demand isolation. But then you need to replace batteries after sometime and also need charger for charging it[which can add to noise]. Its good solution for portable equipment.

But calling the battery is clean linear power is not advisable. I agree that low frequency artifacts are not present in battery power, but chemical reactions taking place do contribute to noise generation, so an amount of decoupling is always needed.

Batteries in this way are easy solution for preamp/phono stages vs costly linear supplies.

 

[kanwar]

Class A is a niche case. But yes, For class A, an SMPS makes a lot of sense as the power drawn by a class A does not vary as much as a class AB.

Another Place where you need a switching power supply is in car audio amplifiers. If you need anything more than 17W or so RMS, you need higher voltages, so step up DC SMPS are used. This is one of those cases where a Linear PSU CANNOT be used

Yes, car PSU can only be done thru SMPS.

Same benefits of SMPS also applies to preamps/phono stages/class-AB amps as well. The implementation then differs and hybrid approach can also be considered with a mix of linear and switching regulators.

 

[hydrovac]

The incursion of switching power supplies into audio
design is obviously going to continue strongly in the
future. The complexity of the product has kept the
higher technology amplifiers with SMPS from outsourcing
yet, but this will come to pass eventually. As
Chinese engineers gain more experience with the opti-
mization of SMPS for audio power amplifier use, the
design cycle of these will probably move there as well.

The magnitude of the task in designing a full-blown switching
power supply, the integration into the audio system and EMI
control require substantial investment.

 

[kapvin]

But calling the battery is clean linear power is not advisable. I agree that low frequency artifacts are not present in battery power, but chemical reactions taking place do contribute to noise generation, so an amount of decoupling is always needed.

Batteries in this way are easy solution for preamp/phono stages vs costly linear supplies.

I didn't know that. Well, one learns new things everyday! thanks.

I think a lot of linear power supplies has to do with the KISS principle. there is not that much thinking required to do an linear acceptable power supply.

I remember when fuel injection cars came into india in a big way post euro 2 norms in 2000; a lot of "tuners" would recommend carburettors as the best way to get more power (these tuners had not figured out the ECU and therefore it was easier for them to trash fuel injection). in fact the more bizarre stories involved taking out an mpfi engine from an esteem and doing a carb conversion. - versus today - where every tuners best friend is a laptop and obd2 dongle. (these are true stories - but don't ask me to name the tuners - some are still in business). maybe linear power has the same trajectory.

 

[greenhorn]

if i may go a bit offtopic - there used to be a big argument about regulated PSU's vs unregulated. I recall reading somewhere that regulated had bass impact, but unregulated had extension, or something of that sort?

Since we have some folks here who have some idea about PSU design and audio, would like to ask about their thoughts on that

 

[doors666]

what are some of the techniques used in the SMPSs now a days to suppress the switching noise, emi/rf etc.
Are there chips out there that handle the resonant converters, like there are chips to do the other types of dc-dc converters.

 

[hydrovac]

if i may go a bit offtopic - there used to be a big argument about regulated PSU's vs unregulated. I recall reading somewhere that regulated had bass impact, but unregulated had extension, or something of that sort?

Since we have some folks here who have some idea about PSU design and audio, would like to ask about their thoughts on that

Power-Supply Technologies

There are three principal ways to power an amplifier:
1. A simple unregulated power supply consisting of transformer, rectifiers, and
reservoir capacitors;
2. A linear regulated power supply;
3. A switch-mode power supply.

It is worthwhile to examine the pros and cons of each technology in a little more detail.
1. It is immediately obvious that the first and simplest option will be the most cost-effective, but at first glance it seems likely to compromise noise and ripple performance, and possibly interchannel crosstalk.

2. The amplifier can no longer deliver higher power on transient peaks.
The overall power dissipation for a given output is considerably increased, due to the minimum voltage drop through the regulator system. The response to transient current demands is likely to be slow, affecting slewing behavior.

3. Switch-mode supplies are a prolific source of high-frequency interference. This can be extremely difficult to eradicate entirely from the audio output.
The 100 Hz ripple output is significant. Much more complex and therefore less reliable than unregulated supplies. Dangerous if not properly cased, as high DC voltage is present.
The response to transient current demands is likely to be relatively slow.
Their design is very much a matter for specialists.

The usual claim there is is that linear regulated supplies give 'tighter bass' or 'firmer bass'; If the phrase means anything, it presumably refers to changes in the low-frequency transient response; however, since no such changes can be objectively detected, this appears to be simply untrue. If properly designed, all three approaches can give excellent sound, so it makes sense to go for the easiest solution; with the unregulated supply the main challenge is to keep the ripple out of the audio, which will be seen to be straight forward if tackled logically.

 

[kanwar]

if i may go a bit offtopic - there used to be a big argument about regulated PSU's vs unregulated. I recall reading somewhere that regulated had bass impact, but unregulated had extension, or something of that sort?

Since we have some folks here who have some idea about PSU design and audio, would like to ask about their thoughts on that

With tighter regulation the rise and fall times of the transient in music becomes sharp because you have stiff voltages and they don't sag.

With unregulated supply the fall time which is decay of transient becomes asymmetric due to sag in rail voltage, here the rise time remains sharp but decay time suffers which gives you a feel of so called extension and this only happens when the transformer is under powered. Transients suffer asymmetric slew induced power sag.

With regulated and semi regulated supplies you don't have such asymmetric pattern. What you get is firm and tighter bass which is more 'natural' then what you can hear from a sagging power supply. For an unregulated sagging supply, you have to ensure large enough capacitance bank to get less sag during transients.

Effects of AC ripple in unregulated linear supply:

Effects of rail sagging on transient, limiter employed to limit the peaks.

 

[kanwar]

what are some of the techniques used in the SMPSs now a days to suppress the switching noise, emi/rf etc.
Are there chips out there that handle the resonant converters, like there are chips to do the other types of dc-dc converters.

2 basic resonant converter techniques.

1. Zero-current switching ZCS- The switching happens when the current through the switch is Zero and you won't get any EMI when current is absent. Current waveform becomes sine like and no longer looks like triangular/trapeziodal. This cuts the switching loss and improves efficiency by slowing di/dt [instantaneous rate of change of current vs time]rates.

2. Zero-voltage Switching ZVS-The switching happens when the voltage across the switch is Zero and you won't get any RFI when voltage difference is almost absent. The voltage waveform remains square but the edges are rounded and no longer sharp. Improves switching loss by ensuring less dv/dt [instantaneous rate of change of current vs time]rates.

Resonant Smps are designed using one of the above or mix of both techniques.

There are more than 100 chips floating in the market to do that job. Look for Phase shifted ZVS, LLC resonant, ZVS resonant, ZCS etc. But as i already said the learning curve is very steep to understand this.

The main factors which ensure low RFI/EMI conducted/radiated design are:

1 Use of resonant topologies.

2 PCB layout with groundplanes and specific placement of key switching components and resonant capacitors.

3. 3 Stage PI filter

4. Current fed CCM PFC.

5. Spread spectrum, not using fixed switching frequency and varying it to ensure the radiated emissions end up in broadband rather than narrowband, where they dissipate easily.